Stabilized photographic silver halide emulsions



United States Patent STABILIZED PHOTOGRAPHIC SILVER HALIDE EMULSIONS Charles F. H. Allen and George A. Reynolds, Rochester,

N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application July 1, 1953, Serial No. 365,542

6 Claims. (Cl. 95-7) This invention relates to fog-inhibiting agents and stabilizers for photographic emulsions and to photographic emulsions containing them.

It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog where it is necessary to distinguish between it and the effects of accidental exposure to radiation; in this invention, We are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is of course desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing materials. While antifoggants and stabilizers may protect, to some extent, against such efiects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both.

It is, accordingly, an object of our invention to provide a method for stabilizing photographic emulsions. A further object of our invention is to maintainthe sensitivity and fog of silver halide emulsions at or close to'initial optimum values under keeping conditions of high temperature and humidity. A further object is to provide photographic silver halide emulsions containing antifoggants or stabilizers Other objects will become apparent from a consideration of the following description and examples.

The above objects are, in general, accomplished by adding to the photographic emulsion certain organic compounds of the following general formula:

wherein R represents-a hydrogen atom or an aromatic group, such as phenyl, 0-, mand p-aminophenyl, o-, mand p-carboxyphenyl, o-, m-. and-p-sulfophenyl, o-, mand p-chlorophenyl, o-, mand p-tolyl, o-, mand p-methoxyphenyl, o-,

mand p-hydroxyphenyl, etc. (e. g. a

mononuclear aromatic group of the benzene series), R1 represents a hydroxyl group or an amino group, such as amino, methylamino, ethylamino, n-propylamino, dimethylamino, diethylamino, di-n-propylamino,etc., and R2 represents a mercapto group or an amino group, such as amino, methylamino, ethylamino, n-propylamino, dimethylamino, diethylamino, di-n-propylamino, etc. In general, the compounds represented by the above formula can be prepared according to the method described in Iour. Am. Chem. Soc., vol. 72 (1950), page 1816, i. e. compounds of the above formula wherein R is an aromatic group.- Compounds wherein R is a hydrogen atom can be prepared according to the process described in U. S. Patent No. 2,407,204, issued September 3, 1946. See also Parker and Webb U. S. Patent 2,543,333, issued February 27, 1951.

The fog inhibitors which we propose to use are added to the emulsion during the process of manufacture, to avoid loss of sensitivity and to inhibit the growth of fog with passage of time under non-ideal conditions of storage.

A solution of the compounds of the invention when added in suitable concentration, before coating, to unsensitized, chemically sensitized, or optically sensitized photographic emulsions does not appreciably affect the sensitometric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are made at appreciable intervals of time, at elevated temperatures and dry or somewhat humid conditions, these compounds do stabilize photographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations: (1) the emulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsion from excess soluble salts, usually by washing, and (3) the second digestion or after-ripening to obtain increased sensitivity. (Mees' The Theory of the Photographic Process, 1942.) We prefer to add the foginhibiting agents after the final digestion or after-ripening, although they can advantageously be added prior to digestion.

Listed below are a number of compounds coming within the scope of the above general formula, which we have found to be particularly advantageous in practicing our invention. These compounds belong to a group of compounds which We shall designate as pentazaindenes.

i N ENTKN Q 5-amino7-hydroxy-2-pheny1-1,2,3,4,6pentazaindene 2. N H:

E-amino-Z-p-carboxypheny1-7-hydroxy-1,2,3,4,6-pentazalndene 4. IIIH:

5 ,7-diamino-2-phenyl-L2,3,4,6-pentazaindene Patented July 19, 1955 7 -amino-5-dimethylamino-2-pheny1-1,2,3,4,6-pentaza1ndene 2-p-aminophenyl-5-amino-7-hydroxy-1,2,3,4,6-pentazaindene 8. (II'H HZNTKNAN/ 5-amino-7-hydroxy-2-p-methoxypheny1-1,2,3,4,6-pentazaindene N N k N- Cl HzN- N N/ -amino-2-p-ch10rophenyl-Y-hydroxy-l,2,3,4,6-pentazaindene 5-a1nino2-hydro-7 -l1ydroxy-1,2,3,4,6-pentazaindene The photographic emulsions used in practicing our invention are generally of the developing-out type; also, it is to be understood that photographic emulsions of varying halide content can advantageously be used. The

antifoggant compounds used in our invention have been found particularly useful when employed in conjunction with geiatino-silver bromiodide emulsions, although they can also be advantageously employed for stabilizing other silver halide emulsions, such as gelatino-silver chloride, bromide, chlorobromide, chlorobromiodide, etc. The emulsions can be unsensitizcd, or sensitized with chemical sensitizers or optical sensitizers. Sulfur sensitizers, such as those disclosed in Sheppard U. S. Patent 1,574,944 can advantageously be added to the emulsions in the conventional manner. Also, various gold sensitizers can be employed in the photographic emulsions stabilized according to our invention.

The antifoggant and stabilizing action was determined by incubation of the emulsions for the times given in the table below at a temperature of 120 F. and relative humidity of percent. The efficiency of the various antifoggants was determined by measuring the speed, gamma and fog of the incubated emulsions containing an antifoggant and comparing these measurements with those of the same batch of emulsion before incubation. Also similar measurements were made on a photographic emulsion containing no antifoggant, both before and after incubation. The tests were made using a high speed silver bromiodide emulsion exposed on an Eastman Type lb sensitometer and developed for 5 minutes in a developer of the following composition:

G. N-methylp-aminophenol sulfate 2.5 Hydroquinone 2.5 Sodium sulfite (desiccated) 30 Sodium metaborate 10 Potassium bromide 0.5 Water to 1 liter.

Anmog Fresh Test Incubation Test No. 42:. 454 4 pound t Fog i 7 02 speed speed None 2,300 1.04 .04 2,100 0.91 .14 2 .027 2,550 0. 92 .04 2,051 0.91 .10 None 3,250 0.85 .04 2,900 0.07 .11 3 .054 3,100 0.86 .04 2,700 0.08 .07 3 .540 2,650 0.87 .04 2,900 0.04 .05 None 2,300 0.92 .07 840 0.50 .74 10 0.6 2,100 0.89 .12 1,780 0.70 .20

The time of incubation for Example 1 was one week,

whereas it was two weeks in Examples 2 and 3.

In a manner similar to that illustrated in the above examples, other pentazaindenes selected from those represented by the above general formula can be incorporated in photographic emulsions for the purpose of stabilization. The fog-inhibiting agents useful in practicing our invention can be used in various kinds of photographic emulsions. In addition to being useful in ordinary nonsensitized emulsions, they can also be used in orthochromatic, panchromatic and X-ray emulsions. If used with sensitizing dyes, they can be added to the emulsion before or after the dyes are added. Suitable dispersing agents for the silver halide emulsions stabilized according to our invention comprise gelatin, or other colloids, such as collodion, albumen, cellulose organic derivatives, synthetic resins, etc.

The optimum amount of fog-inhibiting agent can be determined by making the customary tests employed in emulsion making. Of course, the optimum amount for a given emulsion will vary depending on the presence of emulsion addenda, such as chemical sensitizers, optical sensitizers, etc. In general, we have found that from 0.01 to 5.0 g. of fog-inhibiting agent per mole of silver halide is sufiicient for the purposes of our invention.

Instead of adding the fog-inhibiting agent directly to the photographic emulsion, it is sometimes desirable to incorporate the fog-inhibiting agent in a separate layer which is placed in contact with the silver halide emulsion layer which is to be stabilized. Under such conditions, of course, it is advisable to use a higher concentration of fog-inhibiting agent than indicated above.

In those instances wherein R of the above general formula represents a hydrogen atom, the compounds can alternatively be Written in the following form:

wherein R1 and R2 each have the values given above. Such a structure is formulated in U. S. Patent 2,407,204, mentioned above. Thus compound 10 above would be written as follows:

We have also found that compounds embraced by the first general formula given above wherein R1 represents an alkyl group, such as methyl, ethyl, etc., and R2 represents a hydroxyl group or an alkyl group, such as methyl, ethyl, etc., can also be used in photographic emulsions for the purpose of stabilization. Additional compounds which can thus be employed include, for example, the following:

N N i N CHZOHPOH H1N m N/ What we claim as our invention and desire secured by Letters Patent of the United States is:

l. A photographic silver halide emulsion containing a compound selected from those represented by the following general formula:

wherein R represents an aromatic group of the benzene series, R1 represents a member selected from the group consisting of a hydroxyl group and an amino group, and R2 represents a member selected from the group consisting of a mercapto group and an amino group.

2. A photographic silver bromiodide emulsion containing a compound selected from those represented by the following general formula:

wherein R represents a mononuclear aromatic group of the benzene series, R1 represents a member selected from the group consisting of a hydroxyl group and an amino group, and R2 represents a member selected from the group consisting of a mercapto group and an amino group.

3. A photographic silver halide emulsion containing a compound having the general formula:

N N N M L 4. A photographic silver halide emulsion containing a compound having the following formula:

N COOH ml: Q

, 5. A light-sensitive photographic element comprising a silver halide emulsion layer and an organic colloid layer contiguous to said emulsion layer, at least one of said layers containing as a stabilizing agent for said emulsion layer a compound selected from those represented by the following general formula:

wherein R represents a mononuclear aromatic group of the benzene series, R represents a member selected from the group consisting of a hydroxyl group and an amino group, and R2 represents a member selected from the group consisting of a mercapto group and an amino group.

6. A photographic silver halide emulsion containing a compound selected from those represented by the following general formula:

IIii W\ R R L wherein R represents a mononuclear aromatic group of the benzene series, R1 represents a member selected from the group consisting of an alkyl group, a hydroxyl group and an amino grou and R2 represents a member selected from the group consisting of an alkyl group, a hydroxyl group, a mercapto group and an amino group.

References Cited in the file of this patent UNITED STATES PATENTS Heimbach Sept. 28, 1948 Fry Sept. 4, 1951 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A COMPOUND SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 